The present invention relates to method and apparatus of measuring a tire uniformity and/or dynamic balance.
There have been known method and apparatus of measuring a tire uniformity and dynamic balance in order to evaluate whether a tire may cause the vibration and acoustic noise of a motor vehicle on which the tire is mounted. When a uniformity measurement is performed, a tire to be tested is rotated with a rotary drum being press-contacted the circumferential surface thereof when it is rotated, and radial and/or thrust force variations are detected. When a dynamic balance measurement is performed, based on a centrifugal force when the tire is rotated, the eccentricity of the tested tire is detected.
An example of the tire uniformity and dynamic balance measuring apparatus is disclosed in Japanese patent Application Provisional Publication No. HEI 11-183298. In the above-described publication, a tire is mounted on a rotary spindle, which is rotatably supported within a spindle housing using ball bearings, and is rotated at a predetermined rotation speed.
Specifically, when the uniformity measurement is performed, the rotary drum is press-contacted with the circumferential surface tested tire at several hundreds Kgf or more, and the tire is rotated together with the spindle. The force variation can be detected by load cells fixed to the rotary drum. Since the load cells detect force based on the deformation thereof, for detecting the force variation at high accuracy, the rotation axis of the tested tire must be prevented from vibrating during the uniformity measurement.
On the other hand, when the dynamic balance measurement is performed, the tire is rotated without the rotary drum. Then, the centrifugal force generated in the tested tire due to unbalance of the tire is detected using the load cells provided between the spindle housing and a base of the apparatus. It should be noted that, during the dynamic balance measurement, the spindle housing should be allowed to vibrate freely.
Accordingly, the conventional tire uniformity and dynamic balance measuring apparatus must include a lock/unlock mechanism for preventing the vibration of the tested tire during the uniformity measurement and allowing the vibration of the tested tire during the dynamic balance measurement, which requires a relatively complicated system.
Furthermore, in order to perform the measurements for wheeled tires, by the conventional apparatus, hub holes of the wheel should be fixed to cylindrically-shaped protruded potions of the spindle unit. The axis of the protruded portions coincides with the rotational axis of the spindle at high accuracy in order to position the wheeled tire.
However, the system limit of the diameter of the hub hole is typically around 0.2 mm, so the system limit of coaxiality between the rotational axis of the tested tire and the rotational axis of the spindle can be up to 0.1 mm. That is, the rotational axis of the tire can be divided from the rotational axis up to 0.1 mm. It is therefore difficult to the dynamic balance and/or uniformity at high accuracy.
The uniformity measurement is defined by JASO C607 standard. In the standard, the rotational speeds of a tested tire is defined to 60 r.p.m., which corresponds to a vehicles speed of approximately 7 kilometers/hour, which might be insufficient to evaluate the tires. It is desirable to measure a high-speed uniformity of tires for evaluating the behavior thereof when a motor vehicle runs at a higher speed.
In particular, the tractive force variation affects the vibration and acoustic noise of a motor vehicle which is driving at a relatively high speed. It is therefore desirable to detect the tractive force variation in the high-speed uniformity measurement.
Moreover, the above-mentioned conventional measuring apparatus rotates the spindle using a belt driving mechanism which employs an endless belt for the dynamic balance measurement. In order to rotate the spindle at the desired revolution speed at high accuracy, inelastic belt, such as a canvas belt, is preferably used as the endless belt. Such an inelastic belt can, however, transmit most of vibrations, caused by friction between the belt and pulleys to which the belt is wound. The vibration is transmitted to the spindle, which makes it impossible to measure the dynamic balance at high accuracy.
In view of the above, an advantage achieved by the present invention is to provide a simple-structured apparatus and method of measuring the uniformity and/or the dynamic balance of a tested tire.
A further advantage of the present invention is to provide an apparatus and/or a method capable of positioning the wheeled tire for the spindle of the apparatus with high accuracy.
A furthermore advantage of the present invention is to provide an improved apparatus and method capable of measuring the uniformity suitable for measuring the high-speed uniformity.
In one aspect of the present invention, there is provided an apparatus for measuring uniformity and dynamic balance of a tire, comprising:
a spindle rotatably supported in a rigidly-supported spindle housing, said tire being fixedly mounted on said spindle, said spindle being rotated when measurement is performed; and
at least one piezoelectric force sensor mounted on a surface of said spindle housing, said at least one piezoelectric force sensor detecting a force generated by rotation of the tire as said spindle is rotated.
The piezoelectric force sensor can detect the force while deforming little. It is therefore capable of detecting the force generated during the dynamic balance measurement although the spindle housing is rigidly supported.
In the preferable embodiment of present invention, there is provided an apparatus for measuring uniformity and/or dynamic balance of a tire, comprising:
a spindle rotatably mounted in a spindle housing via at least one bearing, the tire being fixedly mounted on said spindle; and
at least one radial cylindrical bearing that rotatably supports said spindle in said spindle housing, said radial cylindrical bearing including at least a radial double-row cylindrical bearing.
The radial cylindrical bearing is capable of supporting higher load although the strain of the bearing is lower than a ball bearing. The vibration of the spindle against the spindle housing can be prevented, therefore the force generated in the spindle can be transmitted to the spindle housing with high accuracy.
Preferably, a part of a circumferential surface of said spindle on which said radial cylindrical bearing is to be attached is tapered, an inner surface of said radial cylindrical bearing is tapered such that a cone angle of said inner surface is the same as a cone angle of the tapered part of the circumferential surface of said spindle, and said radial cylindrical bearing is attached to said spindle so that the inner surface of said radial cylindrical bearing tightly fits on said tapered part of the circumferential surface of said spindle.
The inner ring of said radial cylindrical bearing tightly fits to said tapered part of the circumferential surface of said spindle, therefore the vibration of the spindle against the spindle housing can be further prevented.
In the preferable embodiment of present invention, there is provided an apparatus for measuring uniformity and/or dynamic balance of a tire, comprising:
a spindle rotatably mounted in a spindle housing via at least one bearing, the tire being fixedly mounted on said spindle,
wherein said spindle holds the tire between a lower rim attached to said spindle and an upper rim which is arranged oppositely with respect to the lower rim, said upper rim is movable upward and downward with respect to said spindle, said upper rim including a lock shaft downwardly extending from a rotation center of said upper rim, said lock shaft being capable of fitting to a fitting portion formed in said spindle.
Preferably, said spindle is rotatably supported in said spindle housing via a plurality of bearings, and wherein the fitting portion of said spindle is located at substantially a midpoint between two of said plurality of bearings.
Such the measuring apparatus described above can supports both of the fitting portion and the lower portion, so the deformation and displacement of the spindle can be prevented by spreading the concentration of bending stress into two parts. The load which the spindle is receiving can be transmitted to the spindle housing with higher accuracy, so the uniformity can be measured with high accuracy.
In the preferable embodiment of present invention there is provided an apparatus for measuring uniformity and/or dynamic balance of a tire, comprising:
a spindle;
a spindle housing rotatably supporting said spindle;
a lower rim attached to said spindle and an upper rim arranged oppositely to said lower rim, said upper rim being movable upward and downward, and rotatable; and
a lock member for holding said upper rim at a predetermined position,
said apparatus being configured to measure uniformity and/or dynamic balance of the tire, by rotating said spindle with holding the tire using said upper and lower rims,
wherein said upper rim includes a lock shaft downwardly extending from the rotation center of said upper rim, the lock shaft being engageable with said spindle, and
wherein said lower rim includes:
a lock shaft insertion cylinder in which said lock shaft can be inserted; and
a lock member attaching hole formed on the circumferential surface of said lock shaft insertion cylinder, one end of said lock shaft insertion cylinder being fixed to one end of said spindle, said lock member being slidable in said lock member attaching hole in the radial direction of said lower rim, said lock member meshing with locking grooves formed on said lock shaft to lock said lock shaft, and
wherein the length of said lock shaft insertion cylinder in the axial direction of said lower rim is 1-2 times as long as the length of said lock member attaching hole in the axial direction of said lower rim.
According to present invention, the distance between a part where the load in the radial direction is enforced (i.e., a part on which the tire is mounted) and a bearing as fulcrum point for the load can be shortened as possible, therefore the bending moment which the spindle is received can be smaller as possible.
Preferably, the length of said lock shaft insertion cylinder in the axial direction of said lower rim is 1-1.5 times as long as the length of said lock member attaching hole in the axial direction of said lower rim.
In the preferred embodiment of the present invention, there is provided an apparatus for measuring uniformity and/or dynamic balance of a wheeled tire mounted on a spindle rotatably supported in a spindle housing, comprising:
a wheel stand formed on one end of said spindle, said wheel stand including a flat surface portion on which the wheel of the tire is mounted; and
a top adapter attached to and facing the flat surface portion of said wheel stand, said top adapter including an urging member capable of urging the wheel of the tire toward said flat surface portion,
wherein said wheel stand includes a tapered cylinder-shaped protruded portion protruded from the flat surface portion, the protruded portion being inserted in a hub hole of the wheel, the central axis of said protruded portion coinciding with the rotational axis of said spindle, the diameter of said protruded portion being smaller at a portion farther from the flat surface portion,
wherein said top adapter includes a collet member having a cylinder portion, the diameter thereof being slightly smaller than the diameter of said hub hole,
wherein the inner surface of said collet member includes a tapered surface having a taper angle substantially the same as the taper angle of the circumferential surface of said protruded portion of said wheel stand, the diameter of said collet member being smaller at a portion farther from said flat surface portion,
wherein said collet member includes a plurality of slits extending from an end of the collet member facing the flat surface portion of said wheel stand, the slits being substantially in parallel to the central axis of said cylinder portion, and
wherein the wheeled tire can be positioned by pressing said collet member toward the flat surface portion of said wheel stand when the inner surface of said collet member contacts the circumferential surface of said protruded portion of said wheel stand, the wheeled tire being positioned when the outer diameter of said cylinder portion is increased and said cylinder member contacts said hub hole.
In the preferred embodiment of the present invention, there is provided an apparatus wherein said piezoelectric force sensor includes a triaxial piezoelectric force sensor.
Preferably, the tire is rotated by a rotary drum of said apparatus during the uniformity measurement.
In the preferred embodiment of the present invention, there is provided an apparatus for measuring uniformity and dynamic balance of a tire, said apparatus comprising:
a rotatable spindle, the tire being fixedly mounted on said spindle; and
a rotary drum that is press-contactable to the tire, wherein both of said rotary drum and said spindle are rotatably driven, respectively,
said rotary drum being rotatably driven during the uniformity measurement,
said spindle being rotatably driven during the dynamic balance measurement,
said spindle is rotatably driven by a transmission belt, said transmission belt being wound around a driving pulley and at least one driven pulley, at least one of said driving and driven pulleys being movable to engage/disengage said transmission belt with/from a pulley of said spindle,
said spindle is rotatably driven during the dynamic balance measurement when said transmission belt has engaged the pulley of said spindle, and
said spindle is rotatably driven during the uniformity measurement when said transmission belt has disengaged from the pulley of said spindle.
Preferably, said apparatus is capable of measuring the dynamic balance immediately after the uniformity has been measured, and said driving pulley is prerotated and the circumferential speed of said driving pulley is set to the circumferential speed of said pulley of said spindle during the uniformity measurement so that the rotational speed of said spindle is unchanged when said transmission belt engages said pulley of said spindle. Preferably, said transmission belt is wound around all of said driving pulley and said driven pulleys. Preferably, the outer surface of said transmission belt engages with the pulley of said spindle during the dynamic balance measurement.
In the preferred embodiment of the present invention, there is provided an apparatus for measuring dynamic balance of a tire, comprising:
a rotatable spindle, the tire being fixedly mounted on said spindle, said spindle being rotatably supported in a rigidly-supported spindle housing,
wherein a force generated by the rotation of the tire can be detected by a piezoelectric force sensor mounted on a surface of said spindle housing, the tire and said spindle being rotatably driven by a rotary drum which is press-contacted with the tire at a first pressing force in the predetermined direction which is perpendicular to the rotational axis of said spindle and rotating the tire.
Preferably, said first pressing force is within a range of 20-100 kgf. Preferably, said first pressing force is within a range of 40-60 kgf. Preferably, said piezoelectric force sensor is capable of detecting a force component in a direction perpendicular to both of said predetermined direction and the rotational axis of said spindle.
In the preferred embodiment of the present invention, there is provided a method for measuring dynamic balance of a tire, comprising:
a tire mounting step for mounting the tire on a spindle of a dynamic balance measuring apparatus, the spindle being rotatably attached to a rigidly-supported spindle housing of the apparatus;
a first tire pressing step for pressing the tire in a predetermined direction perpendicular to the rotational axis of the spindle at a second pressing force with a rotary drum of the apparatus;
a rotary drum rotating step for rotatably driving the rotary drum;
a first rotary drum speed changing step for accelerating the rotation of the tire to a first rotational speed;
a second tire pressing step for changing the amount of the load for pressing the tire by the rotary drum into a first pressing force; and
a first measurement step for detecting a force generated in the tire in the first measurement step by at least one piezoelectric force sensor fittingly mounted on the spindle housing,
wherein the first pressing force is 1-10 times as large as the second pressing force.
Preferably, first pressing force is 2-4 times as large as the second pressing force. Preferably, the first rotational speed is within a range of 60-3300 r.p.m. Preferably, the first rotational speed is within a range of 60-3300 r.p.m. Preferably, the first rotational speed is within a range of 750-1400 r.p.m.
In the preferred embodiment of the present invention, there is provided a method for measuring dynamic balance and uniformity of a tire, comprising:
a tire mounting step for mounting the tire on a spindle of a dynamic balance measuring apparatus, the spindle being rotatably attached to a rigidly-supported spindle housing of the apparatus;
a first tire pressing step for pressing the tire to a second pressing force by a rotary drum of the apparatus, the rotary drum being capable of pressing the tire in the predetermined direction perpendicular to the rotational axis of the spindle and rotating the tire;
a rotary drum rotating step for rotatably driving the rotary drum;
a first rotary drum speed changing step for accelerating the rotation of the tire to a first rotational speed;
a second tire pressing step for changing the amount of the load for pressing the tire by the rotary drum into a first pressing force;
a first measurement step for detecting a force generated in the tire by at least one piezoelectric force sensor mounted on the spindle housing;
a third tire pressing step for changing the amount of the load for pressing the tire by the rotary drum into a third pressing load;
a second rotary drum speed changing step for changing the rotational speed of the tire into a second rotational speed; and
a second measurement step for detecting a force generated in the tire by said piezoelectric force sensor.
Preferably, said third pressing load is 100-2000 kgf. Preferably, said second rotational speed is 60 r.p.m.
In the preferred embodiment of the present invention, there is provided an apparatus for measuring uniformity and dynamic balance of a tire, wherein said tire and spindle are rotatably driven by said rotary drum to a first rotational speed during the dynamic balance measurement while being pressed by said rotary drum to a first load in a predetermined direction perpendicular to the rotational axis of said spindle,
wherein the tire and said spindle are rotatably driven by said rotary drum to a second rotational speed during the uniformity measurement while being pressed by said rotary drum to a second load in the predetermined direction perpendicular to the rotational axis of said spindle,
wherein said first pressing force is smaller than said first pressing force, and
wherein said second rotational speed is within a range of 60-3300 r.p.m.
Preferably, said first pressing force is within a range of 20-100 kgf. Preferably, said first pressing force is 40-60 kgf. wherein said second pressing force is within a range of 100-2000 kgf. said first rotational speed is within a range of 750-1400 r.p.m.